docs: def _httpResponseToMessage(response, server_url):
      """Adapt a POST response to a Message.
  
      @type response: L{openid.fetchers.HTTPResponse}
      @param response: Result of a POST to an OpenID endpoint.
  
      @rtype: L{openid.message.Message}
  
      @raises openid.fetchers.HTTPFetchingError: if the server returned a
          status of other than 200 or 400.
  
      @raises ServerError: if the server returned an OpenID error.
      """
      # Should this function be named Message.fromHTTPResponse instead?
      response_message = Message.fromKVForm(response.body)
      if response.status == 400:
          raise ServerError.fromMessage(response_message)
  
      elif response.status not in (200, 206):
          fmt = 'bad status code from server %s: %s'
          error_message = fmt % (server_url, response.status)
          raise fetchers.HTTPFetchingError(error_message)
  
      return response_message